Greetings all. I live over on the 7.3 "wing" when I am here. But this isn't my truck and I have a question about the fuel system that is probably pretty basic. I'd appreciate some correction if I'm wrong or confirmation if right from anyone who knows.
I only have some photos, and some of the fuel system is taken apart, but everything looks stock. Truck is a 2017 F-350 (6.7 diesel obviously)
Anyway. If I understand correctly, the main fuel pump is submerged in the tank and is relatively low pressure (lift pump) and moves fuel to the cylindrical filter assembly under the hood where fuel goes in, some gets filtered and on to the CP4 injector pump (many have been replaced with DCRs, but not this one). Excess fuel from the filter housing returns to the tank. Fuel to the CP4 then gets pressurized and supplied to the injectors.
Does that sound right? Did I miss anything? Is there a return from high pressure fuel rails at the injectors? If so, where does that return to?

Thanks so much!!!

 

You basically have it right, here is a diagram for more clarity. Unused fuel is dumped at the Pressure Control Valve and returned through the fuel cooler to the tank.

 

I thiink the diagram has an error



I think the lines indicated as 3 and 4 are reversed


I thought the rail return and engine bay filter return meet on the drivers side engine bay.....then pass thru the fuel cooler...then go to the intank filter/pump module.



this diagram shows the intank pump pressureizing both the rail return amd engine bay fuel filter return in parallel

 

The fuel injector return lines go to the secondary fuel filter through the stupid nipple that always breaks off. The line from the fuel cooler (#5) is the return to the bucket in the fuel tank to keep it full. The PCV dumps to the return line then gets cooled and returns to the tank.

 

the rail return line and the fuel filter return line meet at the lower engine bay drivers side.....then proceed to the fuel cooler...then to the tank


the fuel rail return does not pass thru the fuel filter return in a serail manner

 

Correct

 

You missed a fuel filter, on the 2017+ trucks the primary filter/water separator is actually pre-pump, hence why there are four QCs on top of the tank.



https://www.forddoctorsdts.com/forum...dentification/

So the pump sucks fuel through the prepump primary filter, the fuel is then returned to the tank, pressurized by the low pressure fuel pump (lift pump), sent down the frame rails up to the secondary filter, through the secondary filter and into the CP4. CP4 utilizes the majority of the fuel as lube, some fuel is sent to the top side of the pump for high pressure and onto the common rails, the remainder is returned to the tank via the fuel cooler, passes through a thermal valve as previously noted if too cold it is sent back through the low pressure pump and to the engine if warm enough, sent back to the tank.

The three connections on the 6.7 secondary filter are (going from the back to the front of the truck) a 1/2 inbound fuel from the tank, a 12MM outbound fuel to the CP4 and a 5/16 injector returns.



The secondary filter does not return fuel to the tank. There is no baffling in the secondary filter, so if you disconnect the 5/16 and pressurize the system fuel will come out the 5/16 fitting but with the engine running fuel will normally be passing through the 5/16 fitting.

Inside the top of the secondary filter:





Lastly, in the event of a gel or clogging of the secondary filter there is a bypass on the bottom of the media that will allow pressurized fuel to go to the 12mm output without passing through the filter media.



I have no clue what the pressure differential that triggers the bypass however, the thought is, I believe, between the injector return at the primary and the recirculating valve at the tank most of the fuel being introduced has at least been through the secondary filter before.

 

The diagram is for 11-16 but it is essentially the same minus the DFCM aeriated return hose back to the tank and rather than the Injector return lines Teeing into the Secondary filter supply line they have their own orifice on 2017 and above fuel filters.

 

Yes

11-16 has 2 connections on the engine bay fuel filter…an in and an out.


But

17 thru 19 and probally 20 and later gave three connections on the engine bay filter …an in, and out, and a return that meets with the rail return and heads back to the tank.

 

11-16 has three connection, the injector return is plumbed into the 1/2 in bound fitting.

Note the T fitting here:




Lastly, here is the 17-19 injector return line, you have 8 inputs from the injectors and the 5/16 QC for the small fitting on the secondary filter, I don't see where it goes back to the tank.

 

It doesnt go back to the tank, the only fuel that goes back to the tank is the PCV over flow and direct from the HPFP, hence the reason we add an DPK to that circuit before it returns to the tank. The injector return lines feed back into the HPFP supply line via the secondary filter. The difference between 11-16 and 17-24 is the 11-16 tees into the secondary fuel filter supply line while the 17-24 has its own feed into the secondary fuel filter. All feeds into the secondary fuel filter supply the HPFP.

 

Does anyone know what the inline canister is on the 2020+ return line?



Is it an inline filter?

Interesting the injector return fittings are far easier to make out on the 2020+ return hose.

 

It is a one way valve

 

Gotcha, interesting. Thanks!

 

Also keep in mind on 2017+ the hot return fuel mixes it up at the top of the water filter housing at the tank before it returns to the tank. There is a valve in there to recirculate hot fuel with the cold. Its in that area with the two lines in the middle.